This application claims the benefit of Japanese Application No. 11-052875, filed in Japan on Mar. 1, 1999, which is hereby incorporated by reference.
1. Field of the Invention
The invention concerns a vehicle lamp system, and more specifically is directed to a vehicle headlamp that uses a discharge lamp and can vary its characteristics depending on the speed and steering angle of the vehicle.
2. Discussion of the Related Art
Conventionally, filament light bulbs have been used as light sources in vehicle headlamp devices. Depending on the light bulb structure, a four-lamp or two-lamp type headlamp device is used.
An example of a four-lamp type headlamp device is shown in FIG. 9. The four-lamp type headlamp device 1 is equipped with light bulbs 2 and 3 which are installed side by side on both sides of the front part of the vehicle (in FIG. 9, only the right-side headlamp device is shown). One of the light bulbs 2 emits a so-called high beam (hereafter referred to as xe2x80x9cH beamxe2x80x9d), while the other light bulb 3 emits a so-called low beam (hereafter referred to as xe2x80x9cL beamxe2x80x9d). The respective light bulbs 2 and 3 are accommodated inside a lamp body housing 4, and are lit by electric power supplied by a lighting device (not shown in FIG. 9). Furthermore, the light bulbs 2 and 3 are equipped with respective reflective members 2a and 3a, so that the light emitted by the respective light bulbs 2 and 3 is reflected by the reflective members 2a and 3a, and directed towards the front of the vehicle.
In the headlamp device 1 described above, only the light bulb 3 is lit when in L beam mode, while both of the light bulbs 2 and 3 are lit when in H beam mode. As a result, the H beam that is emitted towards the front of the vehicle has an increased quantity of light relative to the L beam. Accordingly, a driver can discern the increase in the quantity of light and be confident that light quantity in the forward field of vision is sufficient in H beam mode.
In FIG. 10, an example of a two-lamp type headlamp device is shown in which a two-lamp type headlamp device 5 is installed on either side of the front part of a vehicle (only a right side headlamp device 5 is shown in FIG. 10). Each of these headlamp devices 5 is equipped with only a single light bulb 6. The light bulb 6 generally has a double-filament structure equipped with two filaments 6a and 6b for emitting the L beam and H beam, respectively. Furthermore, the light bulb 6 is accommodated inside a lamp body housing 4, and is equipped with a reflective member 6c that directs light towards the front of the vehicle. A lighting device (not shown in FIG. 10) supplies electric power to the lamp.
In the headlamp device 5 as described above, power can be switched to the filament 6a in the light bulb 6 so that an L beam is emitted from the filament 6a. In H beam mode, power is switched to the filament 6b so that an H beam is emitted from the filament 6b. 
In the case of a so-called H4 type halogen lamp, which is a lamp commonly used as the light bulb 6, the lamp is constructed so that 55 W of lamp electric power is consumed by the filament 6a in L beam mode, and 60 W of lamp electric power is consumed by the filament 6b in H beam mode, at the rated voltage. As a result, the area illuminated by the H beam is larger than that illuminated by the L beam. Accordingly, the quantity of light in the forward field of vision is detectably increased by the 5 W increase in electric power.
In recent years, discharge lamps such as metal halide lamps, etc., which are advantageous in terms of brightness and longevity, etc., have begun to see practical use as light sources in vehicle headlamp devices in place of conventional halogen light bulbs. In the case of the four-lamp type headlamp device 1, the headlamp can be constructed in the same manner as a headlamp that uses conventional halogen light bulbs, except discharge lamps are used instead of light bulbs 2 and 3, respectively. It is also possible to change only one of the light bulbs 2 or 3 to a discharge lamp. A headlamp that includes a discharge lamp incorporated into the L beam/H beam switching feature also provides similar operator comfort when switching between the H beam and L beam modes as in the case of halogen lamps.
Because discharge lamps are more expensive than halogen light bulbs, the use of discharge lamps in a two-lamp type headlamp device 5 would make it possible to reduce costs as compared to a four-lamp type headlamp device 1. However, discharge lamps emit light by means of an xe2x80x9carc light sourcexe2x80x9d, in which it is physically impossible to install two arc light sources, e. g., for H beam and L beam use, inside a single discharge lamp. As shown in FIG. 11, a two-lamp type headlamp device 5 using discharge lamps is conventionally constructed so that L beam/H beam switching is accomplished by moving a portion 8a of a hood 8 to block direct light from the discharge lamp 7, or moving the discharge lamp 7 itself. Specifically, in the case of the L beam, a portion 8a of the hood 8 is extended as shown in FIG. 11(A), so that the light-blocking area is expanded. As a result, the light directed towards a reflective member region 9a which reflects light into the distance is blocked, and light emitted into the distance (and possibly incident to oncoming vehicles) can be avoided. When H beam mode is desired, the portion 8a of the hood 8 is withdrawn as shown in FIG. 11(B), such that the light-blocking area is contracted. As a result, light is directed onto the region 9a of the reflective member 9 and an H beam is emitted into the distance by the reflective member 9. The discharge lamp 7 is typically a 35 W lamp.
In the two-lamp type headlamp device 5 using a discharge lamp 7 constructed as described above, the quantity of light produced in the H beam mode may be insufficient. In order to compensate for this insufficiency in the quantity of light, an auxiliary reflective part 9b is installed outside of region 9a of the reflective member 9, as shown by the dotted line in FIG. 11.
As shown in FIG. 12, light distribution control of lamp illumination in the direction of a vehicle""s travel path during cornering is accomplished by distributing a portion of the light beam generated by the headlamp device toward the direction of travel for the vehicle in accordance with the vehicle speed and steering angle. Such light distribution control is accomplished by a reflective member 9 constructed, for example, as shown in FIG. 12. The reflective member 9 is split into two parts (upper and lower) along a horizontal direction. The lower part 9c of the reflective member 9 is fastened in place, while the upper part 9d is pivoted about a rotating shaft 9e. The system is arranged so that a portion of light is distributed in the direction of vehicle travel by pivoting upper part 9d about the rotating shaft 9e in accordance with the steering angle. However, in the case of such light distribution control, the illumination of the forward field of vision drops during cornering as a result of the upper part 9d pivoting so that a portion of the light from the discharge lamp 7 is distributed, thus resulting in an insufficient quantity of light in the forward direction of the vehicle. Furthermore, when light distribution control is used in a two-lamp type headlamp device 5 using a discharge lamp 7, L beam/H beam switching is accomplished by means of the discharge lamp 7 equipped with a single arc light source. Accordingly, it is necessary to equip the reflective member 9 with an auxiliary reflective part 9b in order to compensate for the insufficient quantity of light in H beam. Consequently, the number of parts is increased such that the cost of manufacturing and the overall size of the headlamp device 5 is increased.
In light of the above points, an object of the invention is to provide a vehicle headlamp device which is designed so that the quantity of light in the forward field of vision during cornering and in the H beam mode is acceptable. Another object of the invention is to provide a lamp that has good light quality and is constructed at low cost and by means of a simple construction.
According to a first aspect of the invention, the above-mentioned objects can be achieved by a vehicle headlamp device including a light source connectable to a front of the vehicle and configured to produce a light beam, means for switching between a high beam and a low beam located adjacent to said light source, means for broadening a horizontal light distribution of said light beam in a direction of travel of the vehicle during cornering, said means for broadening a horizontal light distribution located adjacent said light source, and a lighting device configured to receive a vehicle speed detection signal and a steering angle detection signal, said lighting device controlling electric power to said light source and said means for broadening a horizontal light distribution, such that electric power supplied to said light source increases, and said horizontal light distribution is broadened in the direction of travel of the vehicle, when the vehicle speed detection signal and the steering angle detection signal exceed predetermined values.
According to this aspect of the invention, a larger electric power is supplied to the discharge lamp when the horizontal light distribution is broadened by means for changing light distribution. Accordingly, when the horizontal light distribution is broadened, the discharge lamp is lit by a larger quantity of light, and the quantity of light in the forward field of vision is sufficient to fill the broadened horizontal light distribution. Consequently, good distant visual recognition characteristics are obtained, and a favorable feeling in terms of quantity of light is realized in the forward field of vision.
According to another aspect of the invention, the lighting device increases the electric power in synchronization with operation of the means for broadening a horizontal light distribution.
According to another aspect of the invention, the means for broadening a horizontal light distribution is constructed such that the light distribution is maximally broadened when the steering angle exceeds a predetermined maximum value, and the increase in electric power effected by the lighting device is performed at a constant rate of increase when the steering angle exceeds the predetermined value. In this aspect of the invention, the increase in electric power effected by the lighting device is accomplished using a switching command signal that is sent to the means for changing light distribution when the steering angle exceeds a certain value. Accordingly, the increase in electric power effected by the lighting device is automatically performed as a result of the steering operation of the vehicle operator, so that the operability of the system is improved, and so that the increase in electric power effected by the lighting device is accomplished more reliably.
In accordance with another aspect of the invention, the means for broadening a horizontal light distribution is constructed such that the light distribution is gradually broadened in accordance with the detected steering angle, and the lighting device is configured to control the electric power to gradually increase in accordance with the detected steering angle. In this aspect of the invention, the horizontal light distribution is gradually broadened in accordance with the steering angle. Accordingly, the increase in electric power effected by the lighting device is automatically performed in accordance with the steering angle as a result of the steering operation of the vehicle operator, so that the operability of the system is improved. Furthermore, the increase in the electric power effected by the lighting device can be performed so that an optimal quantity of light can be provided in the forward field of vision to compensate for the broadening of the horizontal light distribution which tends to disperse the light.
According to yet another aspect of the invention, the lighting device returns the electric power to its original value when the detected vehicle speed drops below a predetermined low value. In this aspect of the invention, when the vehicle is stopped, the lighting device reduces the electric power to its original L beam level. As a result, a saving of electric power is realized and consumption of the vehicle battery is reduced. In addition, deterioration of the useful life of the discharge lamp can be prevented.
According to still another aspect of the invention, the lighting device is further controlled so that the electric power supplied to the light source is increased when the light beam is switched to high beam by the means for switching between high beam and low beam. In this aspect of the invention, the discharge lamp is supplied with a larger electric power when the light is switched to the H beam by the means for switching. Accordingly, the discharge lamp is lit by a greater quantity of light when in H beam mode such that the quantity of light in the H beam mode is sufficient and good distant visual recognition characteristics can be obtained.
According to another aspect of the invention, the lighting device includes a microcomputer which increases the electric power of the lighting device based on one of: 1) the detected vehicle speed; 2) the detected steering angle; 3) a beam switching command signal emitted from the means for switching between high and low beam; and 4) a combination of the detected vehicle speed, the detected steering angle and beam switching command signal. In this aspect of the invention, the microcomputer increases the electric power of the lighting device when the steering angle exceeds a certain value, or when the H beam is selected by the means for switching between L beam and H beam, and stops the electric power increase of the lighting device when the vehicle is stopped. As a result, the increase in the electric power effected by the lighting device during cornering or when the H beam is in use can be accomplished using a microcomputer used for common control. Thus, the construction of the headlamp device is simplified, and the cost of the device can be reduced.
According to another aspect of the invention, the increase in electric power effected by the lighting device is approximately a 5% to 20% increase. In this aspect of the invention, the electric power used when in the L beam mode is set at the rated power of the discharge lamp, and electric power is increased by approximately 5% to 20% of the rated power when in the H beam mode. As a result, the L beam and H beam have the highest brightness possible. Furthermore, even when the H beam is in use, the electric power can be maintained within permissible limits relative to the rated power such that deleterious effects on the useful life of the discharge lamp can be minimized. In addition, when the power increase applied during H beam mode is less than 5%, the quantity of light in the forward field of vision may become inadequate. On the other hand, when the power increase exceeds 20%, effects that cause a deterioration in the useful life of the discharge lamp may occur.
According to still another aspect of the invention, the device is constructed as a two-lamp system in which the light source is configured for placement on the right front side of the vehicle and a second left light source is configured for placement on the left front side of the vehicle. In this aspect of the invention, a single discharge lamp can be disposed on each side of a vehicle, and the increase in electric power effected by the lighting device can be performed when the H beam is in use, and during cornering when the L beam is in use. The quantity of light in the forward field of vision is adequate when using such a two-lamp system. During cornering with the H beam in use, the electric power increase of the lighting device has already been performed in accordance with the switching command signal of the means for switching between H beam and L beam. Accordingly, in order to prevent deterioration of the useful life of the discharge lamp, no further increase in electric power is performed when cornering in H beam mode.
According to another aspect of the invention, a first left light source configured for placement on the left front of the vehicle, a second left light source configured for placement on the left front of the vehicle, a second right light source configured for placement on the right front of the vehicle, wherein the light source is configured for placement on the right front of the vehicle and the vehicle headlamp device is constructed as a four-lamp system. In this aspect of the invention, H beam illumination and L beam illumination are accomplished by means of respective single discharge lamps on each side. Electric power supplied to the discharge lamps used in L beam mode is increased during cornering, and electric power supplied to the discharge lamps used in H beam mode is increased when the H beam is in use. Thus, the quantity of light in the forward field of vision is adequate when using the four lamp system.
According to another aspect of the invention, a vehicle headlamp device for connection to a vehicle includes a light source connectable to a front of the vehicle, a vertical light directing structure located adjacent said light source and configured to direct a light beam emitted from said light source in one of a low beam direction in which said light beam is directed away from the front of the vehicle, and a high beam direction in which said light beam is directed away from the front of the vehicle and at a higher vertical angle relative to said low beam direction, a horizontal light directing structure located adjacent said light source and configured to direct a light beam emitted from said light source in one of a normal beam direction in which said light beam is directed away from the front of the vehicle, and a wide beam direction in which said light beam is directed away from the front of the vehicle and at a larger horizontal angle relative to said low beam direction, and a lighting device configured to receive a vehicle steering angle signal and a vehicle speed signal, and to increase electric power to said light source when the vehicle speed signal and steering angle signal exceed predetermined values.